We reported temperature-dependent narrow width effects on electrical characteristics of 28-nm CMOS transistors measured at temperature of 77 K−300 K. At cryogenic temperatures, P-MOSFETs appear to have stronger temperature-induced threshold voltage (V th ) increase and subthreshold swing (SS) reduction than N-MOSFETs, whereas the improvement in drain-induced barrier lowering (DIBL) is more evident in N-MOSFETs. N-MOSFETs show typical reverse narrow effect (RNWEs) in terms of V th roll-off along with SS rise-up with narrowing channel-widths (W G ). In contrast, P-MOSFETs exhibit anomalous RNWE, that is, V th (SS) decreases (increases) with decreasing W G from 3 µm to 0.6 µm and reversely increases (decreases) with further narrowing to 0.3 µm. RNWEs on N-MOSFETs are clearly suppressed at cryogenic temperatures, whereas P-MOSFETs appear to have enhanced anomalous RNWEs in terms of V th and DIBL variations at 77 K.INDEX TERMS Cryogenic CMOS, reverse narrow width effect.